Herein is described flexible electrostatographic imaging members including electrophotographic imaging members (such as photosensitive members, photoreceptors, photoconductors, and the like) and ionographic imaging members, useful in electrostatographic apparatuses, including printers, copiers, other reproductive devices, image on image, and digital apparatuses, and the like. Flexible electrostatographic imaging members can be seamed or seamless belts. They can also be a sheet, a scroll, or being a belt mounted over a rigid drum structure to form a drelt. In embodiments, the photosensitive members have an electrically conductive ground strip layer situated at one edge of the photosensitive member, comprising a conductive filler dispersed in a binder. In embodiments, the binder is a film forming polymer and the conductive filler is lignin sulfonic acid doped polyaniline. In embodiments, the ground strip layer has absolute opacity. In embodiments, the use of lignin sulfonic acid doped polyaniline filler and a film forming polymer binder in the ground strip layer provides a simpler material formulation, and allows the ease of ground strip layer preparation procedures to effect electrical grounding continuity during photosensitive member imaging machine function.
Since the seam of a flexible seamed electrostatographic imaging member belt represents physical and photo-electrical discontinuity of the belt, the seam is seen to manifest itself into a printout defect to impact copy quality. To resolve this problem, the ground strip layer is therefore required to be opaque such that a timing hole can be punched out at a specific location to affect accurate registration of the belt and thereby avoid images formation directly over the seam.
For reasons of simplicity, the descriptions of electrostatographic imaging members will herein after be represented and focused only on electrophotographic imaging members in flexible seamed photoreceptor belt configuration.
Flexible electrophotographic imaging members, including photoreceptors, photosensitive members, or photoconductors, typically include a photoconductive layer formed on an electrically conductive flexible substrate or formed on layers between the substrate and other photoconductive layers. The photoconductive layer is an insulator in the dark, so that electric charges are retained on its surface. Upon exposure to light, the charge is dissipated, and an image can be formed thereon, developed using a developer material, transferred the developed image to a copy substrate, and fused thereto to form a copy or print.
The photoconductive layer may include a single layer or several layers. In embodiments wherein there are two layers, these two layers may include two electrically operative layers positioned on an electrically conductive layer with a photoconductive layer sandwiched between a contiguous charge transport layer and the conductive layer. The outer surface of the charge transport layer is normally charged in the dark with a uniform negative electrostatic charge, and the conductive layer is used as an electrode.
In order to properly form an image on an electrophotographic imaging member surface, the conductive layer must be brought into electrical contact with a source of fixed potential elsewhere in the imaging device. This electrical contact must be effective over many thousands of imaging cycles in automatic imaging devices. Since the conductive layer is often a thin vapor deposited metal over the surface of a flexible substrate, long life cannot be achieved with an ordinary electrical contact that rubs directly against the thin conductive layer causing total wear through the layer. One approach to minimize the wear of the thin conductive layer is to use a grounding brush such as that described in U.S. Pat. No. 4,402,593. However, such an arrangement is generally not adequate to provide extended service runs in copiers, duplicators, and printers.
Still another approach to extend the functional life as well as improving electrical contact between the thin conductive layer of flexible electrophotographic imaging members and a grounding means is the use of a relatively thick, but narrow width, electrically conductive grounding strip layer coated over and in contact with the conductive layer, and adjacent to one edge of the photoconductive or dielectric imaging layer. Generally the grounding strip layer comprises opaque conductive particles dispersed in a film forming polymer binder. This approach to grounding the thin conductive layer increases the overall life of the imaging layer because it is more durable than the thin conductive layer. However, such relatively thick ground strip layers are still subject to erosion and contribute to the formation of undesirable “dirt” in high volume imaging devices. Erosion is particularly severe in electrophotographic imaging systems using metallic grounding brushes, or sliding metal contacts, or grounding blocks. Moreover, mechanical wear through failure in the grounding strip layer is accelerated under exposure to high humidity conditions. Furthermore, the typical grounding strip layer does often comprise complex material compositions and tedious preparation procedures not convenient to formulate.
In systems using a timing light in combination with a timing aperture (a timing hole punched through) in the ground strip layer for controlling various functions of imaging devices and give precision registration, the erosion of the ground strip layer by devices such as stainless steel grounding brushes or sliding metal block contacts is frequently very severe. The result is that the ground strip layer has local totally worn through spots and become transparent. This, in turn, allows light to pass through the worn spots in the ground strip layer and create false timing signals, thereby giving belt registration errors. The final outcome is that the imaging device prematurely shuts down the useful functional life of the belt. Moreover, the opaque conductive particles/debris generated due to abrasion and erosion of the grounding strip layer, tend to drift and settle on other components of the machine such as the lens system, corotron, other electrical components, and the like. This, in turn, adversely affects machine performance. For example, at a relative humidity of 85 percent, the ground strip layer life can be as low as 100,000 to 150,000 cycles in high quality electrophotographic imaging members. Also, due to the rapid erosion of the ground strip layer, the electrical conductivity of the ground strip layer may decline to unacceptable levels during extended cycling.
Incorporation of micro-crystalline silica particles into ground strip layers has produced excellent improvement in wear resistance. Photoreceptors containing this type of ground strip are described in U.S. Pat. No. 4,664,995. However, due to their extreme hardness, concentrations of silica over about 5 percent in ground strip layers have caused ultrasonic welding horns to rapidly wear as the horn is passed over the ground strip layer during photoreceptor seam welding processes. High welding horn wear is undesirable because horn service life is shortened, horn replacement is very costly, and production line down time is increased.
U.S. Pat. No. 4,664,995 discloses a ground strip comprising a film forming binder, conductive particles and microcrystalline silica particles dispersed in the film forming binder, and a reaction product of a bi-functional chemical coupling agent which interacts with both the film forming binder and the microcrystalline silica particles.
U.S. Pat. No. 5,382,486 discloses a ground strip layer comprising an electrically conductive polymer.
U.S. Pat. No. 5,686,214 discloses a ground strip layer having organic fillers therein.
U.S. Pat. No. 4,664,995 discloses a ground strip having inorganic fillers therein.
There still remains a problem of an inconsistency in opacity and very poor quality of conductive graphite particles dispersion in the material matrix of the prior art grounding strip. This affects proper photoreceptor belt registration during machine function. The optical problem of the ground strip formulation has been caused by poor graphite particle dispersion in the material matrix of the ground strip layer. In embodiments, use of lignin sulfonic acid doped polyaniline (Ligno-PANi) dispersed or contained in the polymer binder of grounding strip layer, provides excellent electrical conductivity and meets the ground strip layer opacity requirement. Furthermore, the wear resistance of the formulated ground strip layer is also effectively enhanced by incorporation of an organic or inorganic filler dispersion.